1. Field of the Invention
The present invention relates to a substrate for mounting a semiconductor chip wherein the semiconductor chip is bonded to a surface of the substrate via a resin. The present invention also relates to a semiconductor device using such a substrate.
2. Description of the Related Art
In the prior art, as shown in FIGS. 2 and 3, a semiconductor chip 20 is mounted onto a substrate body 10 made of a ceramic or a resin via a resin of an ACF 30.
The ACF 30 is formed of thermosetting resin such as epoxy resin or thermoplastic resin such as polyethylene. If the ACF 30 is composed of thermosettable resin, the semiconductor chip 20 could be bonded onto a surface of the substrate body 10 via the thermosettable resin of the ACF 30 which is heated to be cured. On the other hand, if the ACF 30 is composed of thermoplastic resin, the semiconductor chip 20 could be bonded onto a surface of the substrate body 10 via the thermoplastic resin of the ACF 30 which is heated and then cooled to be hardened.
Together therewith, conductor bumps 22 such as Au bumps or others formed on a plurality of electrodes orderly arranged on a surface of the semiconductor chip 20 are electrically connected to a plurality of conductor pads 50 provided on a surface of the substrate body 10 at positions corresponding to the respective conductor bumps by the metallization or the etching of copper foil, via conductive particles (not shown) contained in the resin of the ACF 30.
Thus, the semiconductor chip 20 is surface-mounted onto the substrate via the resin of the ACF 30.
In this regard, ACF stands for "anisotropic conductive film" which contains conductive particles in the resin thereof. When the semiconductor chip is surface-mounted onto the substrate as described above, the conductive particles contained in the ACF resin are interposed between the conductor bump formed on the electrode of the semiconductor chip and the conductor pad formed on the surface of the substrate body. Thus, the electro-conductivity is imparted to a portion of the ACF interposed between the conductor bump on the semiconductor chip and the conductor pad on the substrate body, whereby the conductor bump of the semiconductor chip is electrically connected with the conductor pad on the surface of the substrate body via the conductive particles contained in that portion of the ACF.
The plurality of electrodes on the semiconductor chip 20 is arranged at a predetermined pitch on the surface of the semiconductor chip 20 on which integrated circuits are formed. Accordingly, the plurality of conductor pads 50 for electrically connecting the electrodes is formed on the surface of the substrate body 10 on which the semiconductor chip 20 is mounted at a predetermined pitch in correspondence to the arrangement of the electrodes.
As shown in FIG. 3, the above-mentioned conductor pad 50 is shaped to be widened strips extending in the lengthwise direction, so that the conductor bump 22 can be electrically connected to the corresponding conductor pad 50 in a reliable manner, even if a position of the conductor bump 22 is somewhat deviated from the aimed one in the lengthwise or widthwise direction of the conductor pads 50 for some reason, which conductor bumps are formed on the electrode of the semiconductor chip 20 to be electrically connected to the conductor pads 50 via the conductive particles contained in the resin of the ACF 30.
For this purpose, the plurality of conductor pads 50 of widened strip-shape is arranged on the surface of the substrate body 10 on which the semiconductor chip 20 is to be mounted, so that a narrow gap 52 having a length corresponding to that of the conductor pad 50 is defined between every adjacent conductor pad 50.
According to the above-mentioned substrate for mounting a semiconductor chip, however, voids are liable to generate anywhere in the resin of the ACF 30 when the semiconductor chip 20 is bonded to the surface of the substrate body 10 via the resin of the ACF 30, which deteriorates the adhesion of the ACF resin and results in the stripping-off of the semiconductor chip 20 from the surface of the substrate body 10 on which the semiconductor chip is mounted via the resin of the ACF 30. Thus, a favorable electrical connection is deteriorated between the conductor bumps 22 formed on the electrodes of the semiconductor chip 20 and the conductor pads 50 formed on the surface of the substrate body 10 connected to each other via the electro-conductive particles contained in the resin of the ACF 30.
A cause of the above-mentioned voids generated anywhere in the resin of the ACF 30 is that gas generating from the resin of the ACF 30 during the heating thereof cannot smoothly pass through the narrow gap 52, between the adjacent conductor pads 50 arranged on the surface of the substrate body 10, in parallel to each other, and having a length equal to the longitudinal length of the conductor pad 50, but a large proportion of the gas continues to dwell in the interior of the resin of the ACF 30 disposed inward of the conductor pad 50 and softened by heating.
Similarly, air left in a gap between complicatedly combined connection lines 12 and/or adhered on a stepped side surface thereof expands by the heating, which cannot smoothly pass through the narrow gap 52, between the adjacent conductor pads 50 arranged on the surface of the substrate body 10 in parallel to each other, but a large proportion of the air continues to dwell in the interior of the resin of the ACF 30 disposed inward of the conductor pad 50 and softened by heating.
Particularly, if the ACF 30 is composed of a quick-curing resin, a heating time necessary for bonding the semiconductor chip 20 to the surface of the substrate body 10 via the resin of the ACF 30 is considerably short, for example, in a range from 20 to 60 seconds, whereby almost all the above-mentioned gas and/or air remains in the interior of the resin of the ACF 30, resulting in the voids anywhere in the resin of the ACF 30.
These are also true of a substrate wherein the conductor bumps 22 formed on the electrodes provided on the surface of the semiconductor chip 20 are electrically connected directly to the conductor pads 50 formed on the surface of the substrate body 10 whilst an underfill (not shown) composed of thermosettable resin or thermoplastic resin is filled in a gap between the semiconductor chip 20 and the substrate body 10 to bond the semiconductor chip 20 onto the surface of the substrate body 10.
That is, in such a substrate, when the underfill composed of thermosettable resin or thermoplastic resin is heated, gas generated from the underfill or air left in the interior of the underfill and expanding during the heating could not smoothly pass through the long narrow gap 52 without resistance between every adjacent conductor pads 50 arranged on the surface of the substrate body 10 in parallel to each other, but a large proportion of the gas and/or air continue to dwell in the interior of the resin of the underfill disposed inward of the conductor pad 50 and softened by heating. This causes voids anywhere in the underfill resin, which results in the deterioration of adhesion of the underfill resin whereby the semiconductor chip 20 is easily stripped off from the surface of the substrate body 10.
Accordingly, in the substrate wherein the semiconductor chip 20 is bonded to the surface of the substrate body 10 via the underfill resin, it has been impossible to maintain a favorable electrical connection between the conductor bump 22 formed on the electrode of the semiconductor chip 20 and the conductor pad 50 formed on the surface of the substrate body 10.